Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $246.74   6.461%   $262.6819   $262.68   $262.70   $262.70  
  Purchase #2 $227.33   9.111%   $248.042   $248.04   $248.05   $248.00  
  Purchase #3 $118.66   13.397%   $134.5569   $134.56   $134.55   $134.60  
  Purchase #4 $138.96   9.569%   $152.2571   $152.26   $152.25   $152.30  
  Purchase #5 $125.35   13.476%   $142.2422   $142.24   $142.25   $142.20  
  Purchase #6 $27.34   6.562%   $29.1341   $29.13   $29.15   $29.10  
  Purchase #7 $49.83   8.403%   $54.0172   $54.02   $54.00   $54.00  
  7 purchase totals = $934.21       $1,022.9314   $1,022.93   $1,022.95   $1,022.90